<template>

  <div class="todo-footer">
    <label>
      <input type="checkbox"/>
    </label>
    <span>
         <span>已完成{{completeSize}}</span> / 全部{{todos.length}}
        </span>
    <button class="btn btn-danger" @click="deleteAllCompleted">清除已完成任务</button>
  </div>
</template>

<script>
    export default {
      props: {
        todos: Array,
        deleteCompleteTodos: Function,
        selectAll: Function
      },

      computed: {
        completeSize () {
          //// 统计，初始值为0，todos内的每个元素的checked元素为true时统计结果加1，反之加0
          return this.todos.reduce((preTotal, todo) => preTotal + (todo.complete?1:0) ,0)
        },

        checkAll: {
          get () { // 决定是否勾选
            //计算属性值
            return this.completeSize===this.todos.length && this.completeSize>0
          },

          set (value) {// 点击了全选checkbox  value是当前checkbox的选中状态(true/false)
            this.selectAll(value)
          }
        },
      },

      methods: {
        deleteAllCompleted () {
          if(window.confirm('确定清除已完成的吗?')) {
            this.deleteCompleteTodos()
          }
        }
      }
    }
</script>

<style>
  .todo-footer {
    height: 40px;
    line-height: 40px;
    padding-left: 6px;
    margin-top: 5px;
  }

  .todo-footer label {
    display: inline-block;
    margin-right: 20px;
    cursor: pointer;
  }

  .todo-footer label input {
    position: relative;
    top: -1px;
    vertical-align: middle;
    margin-right: 5px;
  }

  .todo-footer button {
    float: right;
    margin-top: 5px;
  }

</style>
